Uninterruptible power supply (UPS) systems typically have backup power supplied by batteries. For example, referring to FIG. 1, a UPS system 10 includes power circuitry 12, a power relay mechanism 14, and a battery pack 16. The battery pack 16 includes multiple batteries connected in series to supply DC voltage to the power circuitry 12. The mechanism 14 connects the circuitry 12 to the battery pack 16 to supply power from the battery pack 16 to the circuitry 12, to supply from the circuitry 12 to the battery pack 16, and can disconnect the circuitry 12 from the battery pack 16 to inhibit energy transfer between the circuitry 12 and the battery pack 16.
The mechanism 14 acts as a breaker or switch to act as a disconnecting means, e.g., as required by safety codes because a source of power (here, the battery pack 16) must be disconnected from the power circuitry 12 during an emergency, or for non-code purposes such as maintenance of the UPS system 10. The mechanism 14 can comprise a circuit breaker (with or without a fuse) or a switch 20 (as shown) with a fuse (not shown) to provide desired protection. The term “switch” is used below, but this term refers to a switch or a breaker, as appropriate. The mechanism 14 can disconnect the battery pack 16 from the circuitry 12, e.g., at the end of a discharge cycle when AC power is not available to the power circuitry 12, to help prevent deep discharge of the batteries in the battery pack 16 to thereby help prevent damage to the batteries.
To disconnect the power circuitry 12 from the battery pack 16, the mechanism 14 includes an under-voltage relay (UVR) coil and/or a shunt trip (ST) coil 18. The ST/UVR 18 is controlled by a control voltage VC. The control voltage causes the UVR/ST 18 to actuate the breaker/switch 20 to disconnect the circuitry 12 from the battery pack 16. An ST is typically used to disconnect the circuitry 12 from the battery pack 16 in times of emergency (providing emergency power off (EPO) functionality). The UVR can also open the breaker/switch 20 in response to the voltage provided by the battery pack 16 dropping below a threshold voltage.
The mechanism 14 is configured such that when the switch 20 is opened, the switch 20 must be closed manually to reconnect the battery pack 16 to the power circuitry 12. Manually closing multiple battery switches after a loss of power is prone to human error. An operator must first locate which mechanisms 14 need to be reset, and then properly reset the mechanisms 14. This process is tedious and prone to error. A switch that is not properly reset can substantially reduce the run time of the UPS system 10 and result in damage, e.g., due to deep discharge of battery packs 16.